Ion source and ion implantation apparatus

ABSTRACT

An ion source for improving beam transport efficiency regarding a ribbon beam is provided. The plasma generation container is formed with a beam extraction port at an end thereof. The shielding member plugs the beam extraction port and comprises three or more elongate holes each of which is long in a lateral direction of a ribbon beam to be extracted through the shielding member and which are arranged in the form of an array extending in the lateral direction, wherein a first length one of the elongate holes located in a central region of the array is shorter than a second length of one of the remaining elongate holes located on an end side of the array.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No.JP2018-021919, filed in the Japanese Patent Office on Sep. 2, 2018, thedisclosure of which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

Exemplary embodiments relate to an ion source configured to extract aribbon beam therefrom, and an ion implantation apparatus equipped withthe ion source.

2. Description of Related Art

In recent years, a ribbon-shaped ion beam (hereinafter referred to as“ribbon beam”) which is long in one direction has been used to meet thedemand for larger board size, larger beam current or the like. Forexample, a ribbon beam may be relatively long in a lateral direction andrelatively short in a width (or thickness) direction thereof.

As an example of an ion implantation apparatus capable of handling sucha ribbon beam, there is an ion implantation apparatus described in JP2006-313750A. This ion implantation apparatus comprises a magnetic lensfor uniforming a beam current density distribution in a lateraldirection of the ribbon beam. This magnetic lens has a function oflocally deflecting the ribbon beam in a region having a relatively largebeam current toward a region having a relatively small current.

An ion beam composed of positive ions is a positively electricallycharged beam. In the ribbon beam, a potential (beam potential) tends tobecome higher in a central region of the ribbon beam than in each ofopposed lateral edge regions of the ribbon beam, even when the beamcurrent is the same at any position in the lateral direction of theribbon beam.

In a transport path of the positive ion beam, electrons are suppliedfrom an electron source, for example a plasma flood gun or the like, inorder to suppress divergence of the ion beam due to the space chargeeffect. Many of the electrons in the transport path are drawn toward thecentral region of the ribbon beam having a relatively high beampotential, so that the effect of suppressing the divergence due to thespace charge effect becomes stronger toward the central region of theribbon beam. As a result, the ribbon beam largely diverges in thelateral edge regions of the ribbon beam where the divergence-suppressingeffect is relatively weak, and the beam current becomes smaller ascompared to the central region of the ribbon beam.

In the course of transportation to the magnetic lens, the lateral edgeregions of the ribbon beam subjected to a strong diverging effect willcome into collision with a chamber wall surface defining part of thebeam transport path or with other beam optical element disposed in thebeam transport path, resulting in disappearance. In uniformityadjustment, the magnetic lens is operable to locally deflect the centralregion of the ribbon beam largely so as to compensate for a beam currentin the lateral edge regions of the ribbon beam where the ribbon beam haspartially disappeared. Thus, a large deviation will occur indistribution of traveling directions of the ribbon beam, at positions inthe lateral direction of the ribbon beam, although it is possible toachieve uniformity in beam current in the lateral direction of theribbon beam.

SUMMARY

It is an aspect to provide an ion source for improving beam transportefficiency regarding a ribbon beam, and an ion implantation apparatusequipped with the ion source.

According to an aspect of one or more exemplary embodiments, there isprovided an ion source which comprises a plasma generation containerformed with a beam extraction port at an end thereof, and a shieldingmember plugging the beam extraction port and comprising three or moreelongate holes each of which is long in a lateral direction of a ribbonbeam to be extracted through the shielding member and which are arrangedin the form of an array extending in the lateral direction, wherein afirst length one of the elongate holes located in a central region ofthe array is shorter than a second length of one of the remainingelongate holes located on an end side of the array.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of example embodiments, takenin conjunction with the accompanying drawings of which:

FIG. 1 is a cross-sectional view of an ion source according an exemplaryembodiment;

FIG. 2 is a top plan view of a shielding member of the ion sourcedescribed in FIG. 1;

FIGS. 3A and 3B are explanatory diagrams presenting a relationshipbetween a beam current density distribution and a beam potentialdistribution, with FIG. 3A showing a relationship in the related art andFIG. 3B showing a relationship according to an exemplary embodiment;

FIG. 4 is a sectional view of a modification of an ion source accordingto an exemplary embodiment;

FIG. 5 is a schematic diagram of an ion implantation apparatus accordingto an exemplary embodiment; and

FIG. 6 is a top plan view of a shielding member in a modification of anion source according to an exemplary embodiment.

DETAILED DESCRIPTION

The exemplary embodiments of the present disclosure may be diverselymodified. However, it is to be understood that the present disclosure isnot limited to a specific exemplary embodiment, but includes allmodifications, equivalents, and substitutions without departing from thescope and spirit of the present disclosure and claims.

In an ion source according to various exemplary embodiments, elongateholes are formed in a shielding member, and a length of one of theelongate holes located in the central region of the shielding member isset to be shorter than that of one of the remaining elongate holeslocated on an end portion of the shielding member, so that a beamcurrent becomes relatively small in a central region of the ribbon beamextracted from the ion source. This enables a beam potentialdistribution to be averaged in the lateral direction of the ribbon beam.Thus, it becomes possible to reduce a difference in amount of electronsto be drawn in the lateral direction of the ribbon beam, and thussuppress divergence of the ribbon beam at opposite lateral edge regionsof the ribbon beam, thereby improving beam transport efficiency.

In some exemplary embodiments, the ion source further comprises aplurality of electrodes for extracting the ribbon beam from the plasmageneration container. In such a case, the shielding member may beclamped between the plasma generation container and one of theelectrodes disposed closest to the plasma generation container.

In some exemplary embodiments, one of the electrodes disposed closest tothe plasma generation container may additionally serve as the shieldingmember.

An ion implantation apparatus according to various exemplary embodimentsincludes the above ion source, and a current density distributionadjustor that adjusts a beam current density distribution in the lateraldirection of the ribbon beam.

In the implantation apparatus according to the exemplary embodiments,the ion source improved in beam transport efficiency is used, so that itis only necessary for the current density distribution adjustor tolocally deflect a small amount of ions. As long as the local deflectionamount is small, a large deviation never occurs in the distribution oftraveling direction of the ribbon beam at positions in the lateraldirection of the ribbon beam, even if uniformity adjustment of the beamcurrent density distribution is performed. This ion implantationapparatus makes it possible to attain a beam current densitydistribution having high uniformity in the lateral direction of theribbon beam, and control an ion implantation angle with respect to aboard surface, with a high degree of accuracy.

In the ion source according to the exemplary embodiments, elongate holesare formed in the shielding member, and the length of one of theelongate holes located on the central region is set to be shorter thanthat of one of the remaining elongate holes located on the end portion,so that the beam current becomes relatively small in a central region ofthe ribbon beam extracted from the ion source. This enables a beampotential distribution to be averaged in the lateral direction of theribbon beam. Thus, it becomes possible to reduce a difference in amountof electrons to be drawn, in the lateral direction of the ribbon beam,and thus suppress divergence of the ribbon beam at opposite lateral edgeregions of the ribbon beam, thereby improving beam transport efficiency.

With reference to FIGS. 1 and 3, the configuration of an ion sourceaccording to an exemplary embodiment will now be described.

The ion source 1 is configured to extract a ribbon beam therefrom, andis equipped with a cube-shaped plasma generation container 11 which islong in a Y direction indicated in FIGS. 1 and 2, and is formed with abeam extraction port H in a face thereof. FIG. 1 is a cross-sectionalview depicting the ion source, taken along a plane at a central positionin a lateral direction of the ion source.

One face of the plasma generation container 11 is provided with a gasintroduction port 12 for introducing gas into the plasma generationcontainer 11 therethrough. For example, the gas introduction port 12 maybe provided in a top wall of the plasma generation container 11.However, this is only an example and the face on which the gasintroduction port 12 is provided is not particularly limited as long asthe gas may be introduced into the plasma generation container 11.Further, another face (front or rear wall) of the plasma generationcontainer 11 facing in the Y direction mounts thereon a cathode C, suchas a filament, for emitting electrons for ionizing the introduced gas togenerate plasma inside the plasma generation container 11. For example,the another face may be a front wall or rear wall of the plasmageneration chamber 11. However, this is only an example and the anotherface is not particularly limited as long as the cathode C may emitelectrons for ionizing the introduced gas to generate plasma inside theplasma generation container 11. Furthermore, yet another face of theplasma generation container 11 facing in a Z direction is formed with abeam extraction port H for communication between an inside and outsideof the plasma generation container 11. For example, the beam extractionport H may be formed in the bottom face of the plasma generationcontainer 11 in FIG. 1.

This ion source is an electron impact type ion source comprising anelectromagnet (not shown) provided outside the plasma generationcontainer 11 to form a magnetic field inside the plasma generationcontainer 11 along a longitudinal (length) direction of the plasmageneration container 11.

An extraction electrode system E is disposed downstream of the beamextraction port H (on one side of the beam extraction port H facing inthe Z direction). The extraction electrode system is composed of aplurality of electrodes, and configured to extract the ribbon beamthrough the beam extraction port H by given energy. Although theelectrodes composing the extraction electrode system E are called,respectively, an acceleration electrode, an extraction electrode, asuppression electrode and a ground electrode, in this order from theside of the beam extraction port H of plasma generation container 11extending in the Z direction therefrom, in some cases, there are variousother terms. Thus, in this specification, these electrodes will bereferred to respectively as “first electrode 14”, “second electrode 15”,“third electrode 16” and “fourth electrode 17”.

Each of the first through fourth electrodes 14 to 17 is formed with oneor more openings (14 a, 15 a, 16 a, 17 a) for extracting the ribbon beamtherethrough.

In the ion source 1 depicted in FIG. 1, a shielding member 13 isdisposed at a position that plugs the beam extraction port H of theplasma generation container 11, and formed with a plurality of elongateholes 13 a, each of which is long in the Y direction, as described indetail later with reference to FIG. 2.

In this exemplary embodiment, two protrusions P are provided,respectively, on opposite sidewalls of the plasma generation container11, such that the two protrusions P are opposed to the first electrode14 in the Z direction. That is, the two protrusions P extend in the Xdirection parallel to the first electrode 14 as shown in FIG. 1. A coilspring S is provided and extends between each of the protrusions P andthe first electrode 14, so that the first electrode 14 is elasticallybiased toward the plasma generation container 11 by the coil springs S.

The shielding member 13 is clamped between the plasma generationcontainer 11 and the first electrode 14 by the pressure exerted from thecoil springs S. That is, no fastening member such as a bolt is usedamong the plasma generation container 11, the shielding member 13 andthe first electrode 14. This configuration makes it possible to preventseizing of a fastening member under high temperatures and thus improveworking efficiency during maintenance involving replacement ofcomponents. This configuration also makes it possible to sufficientlyrelease a stress during thermal deformation of the shielding member 13and/or the first electrode 14.

Regarding the shielding member 13, this exemplary embodiment employs aconfiguration in which a part 13 b of the shielding member 13 isdisposed outside the plasma generation container 11. However, in someexemplary embodiments, a configuration may be employed in which theentire shielding member 13 is fitted inside the plasma generationcontainer 11. However, the configuration depicted in FIG. 1 is superiorin that, in the event that replacement of the shielding member 13 isneeded, replacement work for the shielding member 13 is simplified.

FIG. 2 is an X-Y plan view of the shielding member 13 depicted inFIG. 1. The shielding member 13 is formed with five elongate holes 13 a.However, this number of holes is only an example, and the number ofelongate holes may be, for example, three or more. Each of the elongateholes 13 a is long in a lateral direction (the Y direction) of a ribbonbeam to be extracted therethrough, and the elongate holes 13 a arearranged in the form of an array extending in the Y direction. Lengthdimensions (Y-directional dimensions) of the elongate holes 13 a are setdifferently depending on respective positions of the elongate holes inthe array. Specifically, one or more of the elongate holes located at acentral portion of the array is shorter than one or more of theremaining elongate holes located on an end portion of the array. Forexample, in the exemplary embodiment shown in FIG. 2, a center elongatehole 13 a is shorter than the remaining elongate holes of the fiveelongate holes 13 a in FIG. 2.

FIGS. 3A and 3B are explanatory diagrams presenting a relationshipbetween a beam current density distribution and a beam potentialdistribution in the lateral direction of the ribbon beam.

FIG. 3A presents the relationship measured when a ribbon beam isextracted from a single elongate hole as in a related art technique. Aspresented in FIG. 3A, as long as the beam current density distributionis approximately uniform in the lateral direction of the ribbon beam,the beam potential becomes relatively high in the central region of theribbon beam, in the nature of the ribbon beam.

FIG. 3B presents a relationship measured when a ribbon beam is extractedfrom the plurality of elongate holes, according to exemplaryembodiments.

In some exemplary embodiments, supposing that each of the openings 14 ato 17 a of the electrodes 14 to 17 in the ion source depicted in FIG. 1is formed as a single hole, the diameter of each of the openings 14 a to17 a has a size which is large enough to cover all the elongate holes 13a formed in the shielding member 13.

On the other hand, in other exemplary embodiments, supposing that eachof the openings 14 a to 17 a of the electrodes 14 to 17 in the ionsource depicted in FIG. 1 is formed as a plurality of holes, theplurality of holes forming each of the openings 14 a to 17 a correspond,respectively, to the plurality of elongate holes 13 a formed in theshielding member 13. That is, the holes of each of the openings 14 a to17A correspond to the holes 13 a in a one-to-one relationship.

By setting a relationship between the elongate holes 13 a of theshielding member 13 and each of the openings 14 a to 17 a formed in theelectrodes in the above manner, it becomes possible to extract theribbon beam having the beam current density distribution presented onthe left side of FIG. 3B, from the ion source.

The elongate holes 13 a of the shielding member 13 are formed such thatthe length of one or more of the elongate holes 13 a corresponding tothe central region of the ribbon beam is shorter than that of one ormore of the remaining elongate holes 13 a corresponding to each of thelateral edge regions of the ribbon beam.

Further, if it is considered that, in a region between adjacent two ofthe elongate holes in the ribbon beam transport path, two sub-beamsextracted from the adjacent elongate holes spread out to fill a gapbetween the sub-beams, the beam current density distribution indicatedby the solid lines may be replaced with the beam current densitydistribution indicated by the broken lines in FIG. 3B.

In the case where the beam current is reduced in the central region ofthe ribbon beam as in the beam current density distribution indicated bythe broken lines in FIG. 3B, the beam potential is lowered in thecentral region of the ribbon beam, so that it is possible to enable thebeam potential to be averaged over the lateral direction of the ribbonbeam to thereby approximately flatten the beam potential distribution.This makes it possible to reduce a difference in amount of electrons tobe drawn, in the lateral direction of the ribbon beam, thereby improvingbeam transport efficiency.

The beam current density distribution and the beam potentialdistribution presented in FIG. 3B indicate characteristics of the ribbonbeam just before the ribbon beam enters a mass analysis electromagnet inan aftermentioned ion implantation apparatus in FIG. 5.

It should be noted that the ion source 1 is not limited to the aboveexemplary embodiment. FIG. 4 depicts a modification of the ion source 1according to an exemplary embodiment. In the following description ofthe exemplary embodiment of FIG. 4, description of similar elements orcomponents to those shown in FIGS. 1-3 is omitted for conciseness.

In an ion source 1 depicted in FIG. 4, a first electrode 14 isconfigured to additionally serve as the shielding member 13 in FIG. 1.In this case, an opening 14 a of the first electrode 14 is formed as theplurality of elongate holes 13 a depicted in FIG. 2. This ion source 1may also obtain the same effects as those in the ion source 1 accordingto the above exemplary embodiment.

Alternatively, instead of completely removing the shielding member 13 asshown in the exemplary embodiment depicted in FIG. 4, the shieldingmember 13 and the first electrode 14 in the ion source 1 depicted inFIG. 1 may be integrated together as a single integrated component.

In the course of extracting the ion beam, part of ribbon beam collideswith the second electrode 15 to generate secondary electrons. Due to thesecondary electrons, the first electrode 14 is subjected to hightemperatures, so that breaking or crack is likely to occur in the firstelectrode. In the configuration depicted in FIG. 1, the shielding member13 is a member for roughly determining an outer shape of a ribbon beamto be extracted from the ion source. Thus, if breaking or the likeoccurs in the shielding member 13, stability in shape of a ribbon beamto be extracted through the operation of the ion source is spoiled.Therefore, giving priority to stable extraction of the ribbon beam, itis advantageous that the shielding member 13 and the first electrode 14are formed as separate components as in the configuration depicted inFIG. 1.

FIG. 5 depicts an ion implantation apparatus IM equipped with an ionsource according to an exemplary embodiment. This ion implantationapparatus IM comprises the ion source 1, a mass analysis electromagnet2, an analysis slit 3, a deflector U, and a process chamber 4. In theprocess chamber 4, a drive mechanism (not shown) is disposed which isoperable to reciprocatingly convey a holder 6 supporting a board 5, suchthat the holder 6 is moved across a ribbon beam RB in the arroweddirection in FIG. 5.

By using the ion source 1 according to various exemplary embodimentsdescribed herein, it becomes possible to suppress disappearance of apart of the ribbon beam at the lateral edge regions in the lateraldirection of the ribbon beam, and thus reduce an amount of ions to belocally deflected by the current density distribution adjustor U. Aslong as the local deflection amount is small, a large deviation neveroccurs in the distribution of traveling direction (i.e., the Zdirection) of the ribbon beam in the lateral direction of the ribbonbeam, even if uniformity adjustment of the beam current densitydistribution is performed.

In a case where the local deflection amount is relatively large as inthe related art, there is concern that the deflection effect also exertsan influence in a thickeness (i.e., width) direction (X direction) ofthe ribbon beam. By contrast, in the ion implantation apparatusemploying the ion source according to various exemplary embodiments, thelocal deflection amount can be sufficiently reduced compared with therelated art.

This ion implantation apparatus IM makes it possible to attain a beamcurrent density distribution having high uniformity in the lateraldirection of the ribbon beam, and control an ion implantation angle withrespect to a board surface, with a high degree of accuracy.

A ribbon beam to be extracted from the elongate holes may be controlledby using the shielding member of the ion source according to theexemplary embodiments, and transported, such that, at an irradiationposition of the ribbon beam to a board in the ion implantation apparatusdepicted in FIG. 5, traveling directions of the ribbon beam at positionsin the longitudinal (lateral) direction of the ribbon beam becomeapproximately parallel to each other, and the beam current densitydistribution in the longitudinal (lateral) direction of the ribbon beambecomes approximately uniform, as shown in FIG. 3B. This makes itpossible to eliminate the need for adjustment by the deflector.

In this case, even if the ion species or energy of a ribbon beam to beextracted from the ion source is changed to give rise to the need forlocal deflection of the ribbon beam by the deflector, it is onlynecessary to deflect a small amount of ions. This provides anadvantageous effect of being able to lower the capacity of a powersupply for the deflector, and for other components.

A current density distribution adjustor U may have a configuration thatis capable of locally deflecting the ribbon beam in the lateraldirection to adjust the beam current density distribution. Examples of acurrent density distribution adjustor are disclosed in U.S. Pat. No.9,734,982 and U.S. Pat. No. 7,078,714, the disclosures of each of whichare herein incorporated by reference in their entireties.

For example, the current density distribution adjustor U may comprise apair of magnetic poles arranged along the longitudinal direction of theribbon beam to sandwich the ribbon beam therebetween, or a pair ofelectrodes arranged along the longitudinal direction of the ribbon beamto sandwich the ribbon beam therebetween. The current densitydistribution adjustor U may adjust a beam current density distributionin the lateral direction of the ribbon beam.

In the exemplary embodiments, the number of the elongate holes 13 aformed in the shielding member 13 is five. In some exemplaryembodiments, the shielding member 13 may be formed with eight elongateholes 13 a, as depicted in FIG. 6. From a viewpoint of forming aplurality of elongate holes 13 a corresponding to the central region andthe opposite lateral edge regions of the ribbon beam, the number of theelongate holes 13 a may be three or more. Further, the elongate holes 13a need not be formed along the Y direction, but may be formed whilebeing slightly displaced in the X direction.

It is to be understood that the present disclosure is not limited to theabove-described exemplary embodiments, but various other modificationsand changes may be made therein without departing from the spirit andscope thereof as set forth in appended claims.

What is claimed is:
 1. An ion source comprising: a plasma generationcontainer formed with a beam extraction port at an end thereof; and ashielding member plugging the beam extraction port and comprising threeor more elongate holes each of which is long in a lateral direction of aribbon beam to be extracted through the shielding member and which arearranged in the form of an array extending in the lateral direction,wherein a first length one of the elongate holes located in a centralregion of the array is shorter than a second length of one of theremaining elongate holes located on an end side of the array.
 2. The ionsource as recited in claim 1, further comprising a plurality ofelectrodes for extracting the ribbon beam from the plasma generationcontainer.
 3. The ion source as recited in claim 2, wherein theshielding member is clamped between the plasma generation container andan electrode of the plurality of electrodes that is disposed closest tothe plasma generation container.
 4. The ion source as recited in claim2, wherein an electrode of the plurality of electrodes that is disposedclosest to the plasma generation container additionally serves as theshielding member.
 5. An ion implantation apparatus comprising: the ionsource as recited in claim 1; and a current density distributionadjustor that adjusts a beam current density distribution in the lateraldirection of the ribbon beam.
 6. The ion implantation apparatus asrecited in claim 5, wherein the current density distribution adjustorcomprises a plurality of magnetic poles arranged along a longitudinaldirection of the ribbon beam to sandwich the ribbon beam therebetween.7. The ion implantation apparatus as recited in claim 5, wherein thecurrent density distribution adjustor comprises a plurality ofelectrodes arranged along a longitudinal direction of the ribbon beam tosandwich the ribbon beam therebetween.
 8. The ion source as recited inclaim 1, further comprising an extraction electrode system.
 9. The ionsource as recited in claim 8, wherein the extraction electrode systemcomprise a plurality of electrodes.
 10. The ion source as recited inclaim 9, wherein the plasma generation container comprises: twoprotrusions that extend from the plasma generation container in parallelwith the electrodes, and two coil springs, one coil spring providedbetween each of the two protrusions and an electrode of the plurality ofelectrodes that is closest to the plasma generation container.
 11. Theion source as recited in claim 8, wherein the extraction electrodesystem includes the shield.
 12. The ion source as recited in claim 11,wherein the extraction electrode system comprises a plurality ofelectrodes and the shield is formed integrally with an electrode of theplurality of electrodes that is closest to the plasma generationchamber.
 13. An ion source comprising: a plasma generation containerincluding a beam extraction port; and a shield provided in the beamextraction port and comprising a first hole, a second hole, and a thirdhole between the first and second holes, each of the first to thirdholes having a length that is longer than a width thereof and arrangedalong a line in a length direction thereof, the length of the third holebeing shorter a length of one of the first hole and the second hole. 14.The ion source as recited in claim 13, wherein a part of the shield isdisposed outside of the plasma generation container.